Low-temperature cracking is a major form of distress that can compromise the structural integrity of asphalt pavements located in cold regions. A review of an Acoustic Emission (AE)-based approach is presented that is capable of assessing the low-temperature cracking performance of asphalt binders and asphalt pavement materials through determining their embrittlement temperatures. A review of the background and fundamental aspects of the AE-based approach with a brief overview of its application to estimate low-temperature performance of unaged, short-term, and long-term aged binders, as well as asphalt materials, is presented. The application of asphalt pavements containing recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) materials to thermal cracking assessment is also presented and discussed. Using the Felicity effect, the approach is capable of evaluating the self-healing characteristics of asphalt pavements and the effect of cooling cycles upon their fracture behavior. Using an iterative AE source location technique, the approach is also used to evaluate the efficiency of rejuvenators, which can restore aged asphalt pavements to their original crack-resistant state. Results indicate that AE allows for relatively rapid and inexpensive characterization of pavement materials and can be used towards enhancing pavement sustainability and resiliency to thermal loading.

Towards developing a method capable to assess the efficiency of rejuvenators to restore embrittlement
temperatures of oxidized asphalt binders towards their original, i.e., unaged values,
three gyratory compacted specimens were manufactured with mixtures oven-aged for 36 hours at
135oC. In addition, one gyratory compacted specimen manufactured using a short-term ovenaged
mixture for two hours at 155oC was used for control to simulate aging during plant production.
Each of these four gyratory compacted specimens was then cut into two cylindrical specimen
5 cm thick for a total of six 36-hour oven-aged specimens and two short-term aging specimens.
Two specimens aged for 36 hours and the two short-term specimens were tested using an
acoustic emission approach to obtain base acoustic emission response of short-term and severelyaged
specimens. The remaining four specimens oven-aged for 36 hours were then treated by
spreading their top surface with rejuvenator in the amount of 10% of the binder by weight. These
four specimens were then tested using the same acoustic emission approach after two, four,
six, and eight weeks of dwell time. It was observed that the embrittlement temperatures of the
short-term aged and severely oven-aged specimens were -25oC and -15oC, respectively. It was
also observed that after four weeks of dwell time, the rejuvenator-treated samples had recuperated
the original embrittlement temperatures. In addition, it was also observed that the rejuvenator
kept acting upon the binder after four weeks of dwell time; at eight weeks of dwell time, the
specimens had an embrittlement temperature about one grade cooler than the embrittlement temperature
corresponding to the short-term aged specimen.

Thin films of paving grade asphalt binders moulded on granite substrates were stressed under rapid cooling and thermal restraint conditions at temperatures ranging from 15°C to -50°C. This temperature range encompasses typical pavement temperatures in colder climates. Differential thermal contraction between the granite substrates and asphalt binders induces progressively higher thermal stress levels in the binders as the temperature drops resulting in thermal crack formation, and the corresponding release of elastic energy in the form of transient stress waves. Using piezoelectric sensors (Digital Wave, Model B-1025), a four-channel acoustic emission (AE) system was used to record the acoustic emission activity during the binder/granite cooling process. It was observed that AE events of high energy clustered around a narrow temperature range. Assuming the cracking temperature (Tcr) to be the temperature at which the AE signal energy exceeds a pre-selected threshold energy level, this AE testing approach was found to be sensitive and repeatable for predicting cracking temperatures (Tcr) in four paving grade asphalt binders processed to two distinct ageing levels. The effect of binder type, ageing level and binder film thickness on cracking temperature is discussed. These AE-based Tcr predictions showed strong correlations with predictions based on either the AASHTO TP1 or the MP1A protocols.

Adhesion levels in laminated safety glass samples, ie windshields, have been assessed using both a non-destructive evaluation method based upon an energy velocity guided wave approach and a commonly used destructive testing method. Laminated safety glass consists of a plastic interlayer surrounded by two glass plates. The interfaces between the plastic interlayer and the two adjacent glass plates are assumed to be imperfect and are modelled using a bed of longitudinal and shear springs. The spring constants are estimated using fracture mechanics in conjunction with surface analysis of the plastic interlayer and of the two adjacent glass plates via atomic force microscopy and profilometer measurements. Energy velocities calculated using this theoretical multilayered model are compared with energy velocity values obtained experimentally using laminated safety glass samples with different adhesion levels. Results show that an energy velocity approach can successfully be used to non-destructively estimate adhesive bond strength in laminated safety glass.